1. Field of the Invention
This invention relates to an improvement on the distance measuring device for a camera capable of measuring distances of a plurality of parts within a photographing field.
2. Description of the Related Art
In automatically detecting a focal point, the conventional photographic camera has been arranged to obtain information on the distance to a photographing object by means of a distance measuring device which performs distance measurement only for the middle part of the photographing field. Therefore, in the event of a picture composition having a main object located at one side of the field, the conventional camera has necessitated the so-called pre-focus operation in which the distance to the object is first measured by placing the main object within a distance measurement mark provided in the middle part of a view finder and then by relocating the object at the desired side position within the field before a photo-taking operation. However, the pre-focus operation is not readily understandable by people unfamiliar with photography. Besides, the improved performance of the automatic focus detecting device of today tends to cause people to forget the necessity of the pre-focus operation and prompts them to perform erroneous photographing operations. Most of blurred pictures result from such negligence.
To solve this problem, an automatic focus detecting device which obviates the necessity of the pre-focus operation by obtaining a plurality of distance measurement data from reflection lights resulting from spot lights projected toward varied spots of the field has been proposed in U.S. patent application Ser. No. 636,590, now abandoned, which has been assigned to the assignee of the present invention. In the case of the device disclosed in this U.S. patent application, however, a main object which is most important to the photographer is handled evenly with subordinate objects. While a picture thus obtained is in focus as a whole, the focus on a specific main object is not sharp enough, because: The plural results of distance measurement are merely averaged and the focal point of a photo-taking lens is adjusted to the averaged distance value. This is a shortcoming of the prior art device. For example, assuming that the automatic focus detecting device arranged to measure the distances of three parts of a field including one middle part and two peripheral parts, only one of the three distance measuring parts may have the main object which is located in the middle part in many cases while other two distance measuring parts are in the background of the field. As a result, the object distance is apt to be detected as a distance much farther than the actual distance.